1. Field of the Invention
The present invention relates to a process and a device for coating a transparent article by spraying thereon a mixture of components capable of forming a protective layer of high optical quality.
2. Description of the Background
Transparent articles, particularly glasses, provided with a plastic protective layer have been described in numerous publications. For example, French Pat. Nos. 2,251,608 and 2,316,913 describe glasses formed from a glass support coated with a plastic layer exhibiting antilaceration properties, and so-called surface properties, in particular resistance to scoring or scratching and abrasion. French Pat. No. 2,230,563 describes articles of high optical quality formed by a plastic support coated with the same plastic layer having properties of resistance to scoring and abrasion.
The protective layer used in the various applications is essentially made up of a thermosetting polyurethane and can be produced by reactive casting of a mixture of components capable of forming polyurethane on a plane support, this layer then being assembled by gluing to the article to be coated.
The layer can also be formed, when the article is prepared by casting directly onto the article or by immersing the article in a bath containing the reaction mixture, or also by spraying the reaction mixture onto the article. But in this case, spraying with spray guns is not entirely satisfactory. This type of spraying generally does not provide a layer of homogeneous thickness and of good optical quality, free of orange peel, because of the differences in viscosity of the components forming the reaction mixture which is to be sprayed. Moreover, these differences cannot be attenuated by using a solvent because the solvent latter is often incompatibe with the plastic to be coated, for example, polycarbonate, and can also cause harmful effects during production of the layer.
Therefore, a need continues to exist for a process and a device for coating treansparent articles in such a manner that the transparent article is coated with a protective layer of high optical quality